In vehicle construction, composite workpieces which are composed of a shaft and an essentially rotationally symmetrical hub part are used in numerous applications. Examples of hubs are transmission and clutch parts or also disk-shaped blanks which are still to be mechanically processed.
It is known to join a shaft and hub part in a connection region by friction welding. In this case, an end face of the shaft is joined to an end face of the hub part in a conventional manner. Alternatively, the shaft and hub part can be joined by means of overlap friction welding; this involves a variant of pressure welding in which, in contrast to conventional end-face friction welding, the surfaces to be joined are arranged at the circumference of the components. In this case, for example, a shaft is welded to a hub part with overlap by one of the two components being set in rotation and being pressed onto the other stationary counterpart. The welding process starts at the contact surfaces of the components. After the plasticization of the material located there by the friction heat, a permanent joint is obtained after the end of the rotary movement.
Shown in DE 199 34 855 C1 is a friction-welded shaft/disk composite workpiece which is assembled from a disk having a through-hole and from a shaft by means of overlap friction welding. During the welding of shaft and disk, annular connection sections are produced, between which annular cavities are formed. A reduction in the weight of the entire part is achieved by the joint sites offset from one another radially and axially, it being possible for the cavities to be used, for example, for directing oil.
In the state of the art shafts and hubs for a composite clutch are connected by a intermeshing toothing between the components to achieve a frictional or positive fitting connection. The use of the clutches is mainly in transfer cases and automatic transmission applications.
Known applications have a so called “tube to tube” joint design. This means that friction welding takes place between two end faces which have a pipe shape. In comparison to the pipe shaped end face of the softer part the harder part has a larger or equal pipe outside diameter and a smaller or equal pipe inside diameter. With other words the harder part has an equal or larger end face than the soft part. This guarantees that the end face of the softer part will always fully touch the end face of the harder part. The harder side keeps being pipe shaped in the joining location, but the softer part has a flat surface in the joining location. This means that the softer part has the larger joining surface (“end face”). This has major advantages in terms of packaging and cost. The end face of the harder part is designed in a way that it is guaranteed that the typical material squeezing out can take place in order to create an atomic bond.